Explosive cartridge for plaster shooting



Nov. 8, 1949 s. H. DAVIDSON 2,437,317

EXPLOSIVE CARTRIDGE FOR PLASTER SHOOTING Filed Oct. 51, 1945 a V B 7 l B V72 S RMUEL H.DAV1DSON aw 4 WM Patented Nov. 8, 194$ EKILOSIVE CARTRIDGE FOB PLAS'IEB SHOOTING Samuel Henry Davidson, assignor to Imperial C West Kilbride, Scotland. hemical Industries Limited, a corporation of Great Britain Application October 31, 1945, Serial No; 625,698

In Great Britain February 9, 1945 (Cl. 102-24l IClaim.

The present invention relates to the provision of blasting explosive cartridges for plaster shoot- For the purpose of breaking boulders into smaller fragments of more convenient size for removal, the operation known as plaster shooting, or mud-caping is often carried out. In this operation a cylindrical cartridge of a detonating explosive, which is frequently of the same nature as the explosives used for bore-hole shooting in quarry blasting. provided with a detonator inserted at its end in the usual way, is pressed with its cylindrical surface along an incipient crack in the boulder, and the cartridge is stemmed by the application of a considerable thickness of clay, mud, sand or the like materials, which should be free from stones, and is then fired. In the case of powder explosives the cartridge is sometimes emptied and the explosive made into a roughly conical heap before the detonator is inserted near the base of the heap and the stemming is applied- The explosive used must have a relatively high velocity of detonation under these conditions of initiation, otherwise, it is inefiective; and disappointing results have frequently been obtained owing to the use of insuflicient stemming material or of explosives incapable of detonating at the required high velocity under these conditions.

It is an object of the present invention to provide a plaster shot blastin cartridge, embodying both a main explosive charge and a. primer, which will enable plaster shooting to be carried out more conveniently and expeditiously, and/or with more effective results than heretofore.

The plaster shot blasting cartridges provided according to the present invention enable stemming to be dispensed with altogether and are adapted to ensure that the explosive will achieve a high velocity of detonation before any considerable amount of it has detonated at low velocity, a result not ordinarily attained with hitherto used plaster shooting assemblies.

According to the present invention a plaster shot blasting cartridge comprises a cylindrical plastic, that is to say permanently deformable: explosive charge capable of developing high velocity detonation at one end of which there is positioned a rigid tubular structure surrounding a high velocity detonation primer in detonation contact with said explosive charge and adapted to receive a commercial detonator at its free end, the said plastic explosive charge, high velocity detonation primer and rigid tubular structure being enclosed in a wrapper of easily rupturable material.

The operator using the plaster shot cartridge holds it with the tubular rigid structure as a hand grip and squashes the other end of the cartridge on to the desired portion of the surface of 2 the boulder with suillcient force to rupture the wrapper and flatten out that end of the cylinder of plastic explosive. Thedetonator, which may belprovided with a suitable length of fuze if it is not an electric detonator, is then inserted into the high velocity primer, and the charge is then ready for firing. The squashing of the end of the cy der of plastic explosive presented to the bo der increases the area of contact substantially; beyond the original cross section of the cylinder and thus ensures the transmission of much of the energy of the explosive to the material of the boulder, and normally causes it to adhere enough to permit of the use of the cartridge on sloping surfaces. The fact that the rigid tubular structure containing the high velocity primer still projects from the surface of the more or less flattened mass of explosive facing the operator's hand also ensures that the detonation' wave will be well developed in a direction favourable to the fragmentation of the boulder, and that a high velocity of detonation will rapidly be attained.

Ezplosives of high power capable of detonating at high velocities when initiated by means of commercial detonators in tampered boreholes may advantageously be used, so long as they are of the requisite permanently deformable plasticity, Plastic explosives based on solutions of nitrocellulose in liquid nitric esters may advantagequsly be used, and many of the available high strength nitroglycerine-nitrocellulose plastic explosives of commerce are very suitable, for instance various gelignites of from about per cent of the strength of Blasting Gelatine upwards, and Polar Ammon gelatine dynamite. Various plastic explosives comprising solutions of nitrocellulose liquid aromatic nitrocompounds are also suitable.

The high velocity detonation primer comprises desirably about an ounce of an explosive capable of being detonated at high velocity by'a commercial detonator without confinement, for instance a pressed guncotton tetryl or trinitrotoluene pellet, or a cast Pentolite primer. The primer is provided with a recess or channel accessible from the end of the cartridge remote from that to be applied to the boulder, for the purpose of receiving the detonator, which may conveniently be an ordinary detonator attached to the end of a length of safety fuze.

The invention is further illustrated in the diagrammatio drawings accompanying the specification whereof Figs. 1 and 2 arerespectively a longitudinal section and a section along AA of Figure 1 of a plaster shot blasting cartridge according to the invention, and Figs. 3 and 4 are respectively a longitudinal section and a section along BB of Fig. 3 of the same plaster shot blast- 3 ing cartridge after it has been squashed against a boulder to be blasted.

Figs. 1-4 like reference numerals refer to the same parts. I is a rigid hollow wooden cylindrical structure adapted to serve as a hand grip. 2 is a high velocity detonation primer, consisting of a one ounce compressed trinitrotoluene pellet, 4

is a hole in the primer adapted to receive a det-" onator, i is a plastic blasting explosive charge of Polar Ammon gelatine dynamite in juxtaposition with and separated from the rigid structure I and the primer 2 by a thin waxed paper septum i. iswaxed paper surrounding the hand grip I and the plastic blasting charge I and folded at the top of the high velocity detonation primer 2 and at the bottom of the explosive charge 5. The waxed paper I is perforated at l, a little above the base of the explosive charge 5. 3 is a layer of colored aper stuck to the wax paper to indicate the 'end of the plaster shot blasting cartridge which the detonator is to be inserted.

0n squashing the plaster shot blasting cartridge against a boulder to be blasted the waxed paper I splits at the perforations I and the ex- 4 plosive charge I is flattened out as illustrated in I Figures 3 and 4.

I claim:

A plaster shot blasting cartridge which comprises a cylindrical permanently deformable plastic explosive charge capable 01' developing high velocity detonation. a high velocity detonation primer adapted at one end to receive a commercial detonator and placed in detonation contact at its other end with the said explosive charge, a rig-id tubular structure surrounding said primer, and a wrapper of easily rupturable material enclosing said plastic explosive charge, said primer, and said rigid tubular structure.

SAMUEL HENRY DAVIDSON.

REFERENCES crrsn The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 196,767 Rand Nov. 6, 1877 273,270 Frothingham Mar. 6, 1883 

